1. Field of the Invention.
The present invention relates generally to improvements in hard disk drives, and, more particularly, but not by way of limitation to improvements in writing servo data to dedicated servo surfaces read by servo transducers for following tracks along which data is stored in the drive.
2. Brief Description of the Prior Art
In hard disk drives used for storing data generated by a computer, the data is written to concentric data tracks defined in magnetizable coatings on the surfaces of rotating disks and is subsequently read therefrom by read/write transducers that are positioned adjacent the surfaces of the disks. The disks are mounted on a common spindle and the read/write transducers are mounted on a common electromechanical actuator that moves the transducers across the disks so that a selected data track can be acquired and subsequently followed using a servo system that reads servo patterns written to the disks and provides positioning signals to the actuator. In one servo system in common use, the servo patterns are written on servo tracks on one disk surface, a dedicated servo surface, at the time of manufacture of the hard disk drive and the servo and data tracks are arranged in concentric cylinders so that following of a data track by a read/write transducer can be effected by following of the servo track in the same cylinder by the transducer, referred to as a servo transducer, adjacent the dedicated servo surface.
As will be clear to those of skill in the art, the integrity of the servo patterns on the dedicated servo surface is critical to the operation of the hard disk drive. For example, should a user's computer access the dedicated servo surface and write data to it, the servo system would no longer be able to properly position the actuator for data track acquisition and following and the drive would become inoperable. In the past, such access has been prevented by preventing a direct connection between the user's computer and the servo transducer, necessary for writing to servo surface, from being made. To this end, the location of the disks, transducers and actuator in a sealed housing that is provided to prevent dust or smoke particles from collecting on the disks and being driven into the transducers which fly only a small distance above the disk surfaces was exploited. Specifically, a connector that was utilized to provide an electrical connection between disk drive circuitry used during writing to the dedicated servo surface was placed within the case so that the user of the disk drive could not access the dedicated servo surface for writing by any electrical connection that might be made to the hard disk drive. Rather, the sole connection that the user might make to the servo transducer was at the output of an amplifier that amplifies data read from the servo surface. Hence, no possibility of writing to the servo surface, after the disk drive left the manufacturer, existed.
A problem with this scheme for isolating the dedicated servo surface with respect to writing is that the housing must be open, to provide access to the connector, during writing of the servo patterns. However, writing the servo patterns while the housing is open presents a second problem. Since the collection of dust and smoke particles on the disks must be avoided, the housing can be opened only in a very clean environment that is not only costly to provide but is an inconvenience to the person writing the servo pattern. In the past, these limitations have been accepted because of the manner in which the actuator was positioned during writing of the servo patterns; specifically, a stepping motor was attached to the actuator and used to position the servo transducer during writing of the patterns. However, it has recently been recognized that the actuator can be positioned for writing servo patterns by alternately writing servo patterns on the servo surface and on a data surface as disclosed in U.S. Pat. No. 4,912,576, issued Mar. 27, 1990 to Donald W. Janz. In the method disclosed by Janz, a servo pattern is written to the servo surface while the actuator is against a stop and this pattern is then used to guide the actuator, with a radial offset, while a servo pattern is written to a data surface. The servo pattern on the data surface is then used to guide the actuator while a second servo pattern is written to the servo surface and the process continues until the servo surface is completely written with servo patterns. Alternatively, the actuator can be positioned with a rod that extends through a sealed hole in the housing. Thus, except for the need to make the dedicated servo surface inaccessible to the disk drive user with respect to writing, the inconvenience and cost of writing the servo patterns in a controlled environment is unnecessary.